One day in modern-day Ginza, Tokyo, a portal from another world suddenly appears and a legion of soldiers and monsters emerge to attack the city. Using more advanced weaponry and tactics, the Japan Self-Defense Forces (JSDF) easily repels the enemy and passes through the Gate to establish a forward operating base and initiate peace negotiations with the Empire of the other world. Yōji Itami is a JSDF officer sent to investigate the other world, where magic, dragons and elves are real, using his knowledge of fantasy stories to make his way in this new environment. While exploring the Special Region, he ends up selflessly aiding its people.